This invention relates generally to welded pipe joints and more particularly to a welded joint for a pipeline including a liner.
In today's world of pipelines it is becoming more and more popular to rehabilitate pipelines than to replace them. One form of pipeline rehabilitation involves relining the host pipe with a high density polyethylene liner. High density polyethylene (HDPE) pipe is a relatively inexpensive pipe and resists material erosion, corrosion and, abrasion while being relatively chemically inert. One common method of installing a HDPE liner is to pass the liner through a series of downsizing roller boxes, each comprising series of concave rollers set about the parameter of the liner. Each set of rollers has a smaller lumen than the one before it. As the HDPE liner is pulled or pushed through the series of roller boxes the rollers exert an external force on the liner about the parameter of the liner. HDPE has the capability of elastic deformation that allows the liner to actually compress in the circumferential dimension. The reduction can be as much as 8% to 12% or possibly even greater (e.g., up to about 25%). This allows the HDPE liner to have an outside diameter 1% to 5% greater than the inside diameter of the host pipe. After passing through the diameter reduction roller boxes the liner has a diameter in the neighborhood of 5% less than the inside diameter of the host. This allows the HDPE liner to be pulled through the host pipe. After the HDPE liner is pulled through, the ends are cut off and with the release of tension the liner returns to near its original diameter and causes tight fit within the host pipe.
After the HDPE has been installed, the ends of the liner and the host pipe must be returned to service by reestablishing the connections at either end of the pipeline. Ways to do this with flange ends have been accomplished by various companies with varying degrees of success, complexity and difficulty. Many pipe lines however are not conducive to using flange ends or spool pieces to reconnect the lined section of the pipe to the pipeline. Many systems owners require a monolithic pipeline which requires welded joints in the pipe line. The instant invention solves the problems associated with this type of joint reconnection. However it can also be used in a flange joining type pipeline system by merely welding a flange on to the described termination end seal below.
Other attempts to provide a welded joint for a lined pipe generally involve the use of numerous components. This is primarily because it is important to assure that a terminal end of the liner be sealed with the pipe so as to prevent ingress of fluid between the liner and the pipe. Pipe liner that is inserted into an existing pipe over significant distances will be subject to significant scarring on the outer surface of the liner because of sliding engagement with the inner wall of the pipe. The scars form paths or channels for ingress of fluid, particularly at the terminal end of the liner. Thus, even if the liner is compressed tightly against the inner wall of the pipe, the channels left by the scarring may well permit fluid to enter between the liner and the inner pipe wall.